1-Acetyl-3'-(4-bromophenyl)-3'-chlorospiro[3H-indole-3,2'-oxetan]-2(1H)-one

In the title compound, C₁₈H₁₃BrClNO₃, the heterocyclic ring of the indole is distorted from planarity towards an envelope conformation. The orientations of the indole, oxetane, chloro and bromo­phenyl substituents are conditioned by the sp³ states of the spiro-junction and the Cl-attached C atoms.

S1. Comment

The compound 1-acetylisatin undergoes photoinduced cycloaddition reactions with a wide range of alkenes. These reactions have become one of the synthetic routes to obtain the corresponding spiroxetane derivatives (Xue et al., 2001; Zhang et al., 2002). The asymmetric alkenes in these reactions give syn- and anticlinal spiroxetanes as a separable mixture by column chromatography. The structure analyses of the spiroxetanes have also been reported by us in previous studies (Usman et al., 2001, 2002). As an extension of our systematic study into these photoinduced reactions, we have isolated the title compound, (I), which was one of the spiroxetanes resulting from such a photoinduced reaction of 1-acetylisatin with β-chloro-4-bromostyrene. An X-ray crystal structure analysis has been undertaken to elucidate its steric configuration and conformation, and the results are presented here. \sch

The bond lengths and angles in (I) (Fig. 1) are within normal ranges (Allen et al., 1987). The C8—C9 bond length of the spiroxetane (C8/C9/C10/O2) is slightly longer than the typical value for Csp³—Csp³ due to the bulky substituents attached to both atoms C8 and C9. The spiroxetane is out of planarity, with atoms O2, C8, C9, and C10 deviating by 0.085 (2), -0.078 (3), 0.074 (3), and -0.080 (3) Å, respectively, from its mean plane, and the dihedral angle between the O2/C8/C10 and C8/C9/C10 planes is 163.0 (3)°.

The orientations of the indole (C1/N1/C2—C8), bromophenyl (C11—C16/Br1) and chloro (Cl1) substituents are conditioned by the Csp³ state of atoms C8 and C9, while the relative distribution of the indole and bromophenyl substituents is determined by the torsion angles of C7—C8—C9—Cl1 - 25.4 (1)° and C1—C8—C9—C11 - 20.8 (3). These indicate the staggered configuration of atoms C8 and C9 joining the two subtituents. The bond angles subtended at atoms C8 and C9 are in the ranges 89.7 (2)–123.7 (3)° and 84.1 (2)–121.1 (2)°, respectively. The oxetane ring and the indole moiety are approximately orthogonal, corresponding to an angle of 81.1 (2)° between their mean planes, and the planar bromophenyl substituent makes a dihedral angle of 42.9 (2)° with respect to the mean plane of the oxetane ring.

The indole moiety is out of planarity, with the heterocyclic ring being distorted from planarity towards an envelope conformation. Atom C1 is displaced by 0.216 (3) Å from the N1/C2/C7/C8 plane, and the ketone atom O1 attached to C1 deviates by 0.331 (2) Å from the mean plane of the heterocyclic ring. The mean plane of the heterocyclic ring makes an angle of 7.1 (2)° with the benzene ring (C2—C7).

In (I), the acetyl group (O3/C17/C18) attached at N1 is twisted by an angle of 5.1 (1)° from the mean plane of the indole moiety. This indicates that the acetyl group tends to be coplanar with the indole moiety, as usually observed in 1-acetylindole (Usman et al., 2002), due to the interactions of the π-conjugation of the acetyl group. The intramolecular C3—H3···O3 interaction (Table 2), which forms a six-membered closed ring, O3/C17/N1/C2/C3/H3, also participates in the π-conjugation.

As seen in Fig. 1, atom C8 is the S chiral centre and atom C9 is the R chiral centre. However, the centrosymmetric crystal space group indicates that the photoinduced cycloaddition reaction of both achiral 1-acetylisatin and β-chloro-4-bromostyrene gives the racemate spiroxetane mixture of (I).

The molecules of (I) are packed into columns along the b direction (Fig. 2). There are weak intermolecular π···π interactions observed in the crystal, involving the centroid of the benzene ring of the indole moiety. The π···πⁱ [symmetry code: (i) x, -1/2 - y, z - 1/2] and π···πⁱⁱ [symmetry code: (ii) x, -1/2 - y, 1/2 + z] distances are 3.825 (5) Å for both interactions, and the perpendicular distances are 3.392 (5) and 3.535 (5) Å, respectively.

S2. Experimental

A solution of 1-acetylisatin (0.05 M) in the presence of an excess of β-chloro-4-bromostyrene in benzene solution was irradiated with Pyrex-filtered light. After completion of the reaction, the solvent was removed in vacuo and the residue was separated using chromatography on a silica-gel column to afford (I). Single crystals suitable for the X-ray diffraction study were obtained by slow evaporation of an acetone-petroleum ether (3:1, v/v) solution.

S3. Refinement

The H atoms were geometrically fixed and treated as riding on the parent C atoms, with C—H = 0.93–0.97 Å and U_iso(H) = 1.2 U_eq(C). The highest peak and the deepest hole were found near atom Br1, at distances of 0.94 and 0.86 Å, respectively.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL, PARST (Nardelli, 1995) and PLATON (Spek, 1990).

Figures

	Fig. 1. The structure of (I) showing 50% probability displacement ellipsoids and the atom-numbering scheme. H atoms are drawn as small spheres of arbitrary radii and the intramolecular hydrogen bond is shown as a dashed line.
	Fig. 2. A packing diagram for (I) viewed down the b axis.

1-Acetyl-3'-(4-bromophenyl)-3'-chlorospiro[1H-indole-3,2'-oxetan]-2(3H)-one

Crystal data

C18H13BrClNO3	Dx = 1.551 Mg m^−3
Mr = 406.65	Melting point: 382(1)K K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 18.5810 (5) Å	Cell parameters from 4889 reflections
b = 12.5906 (4) Å	θ = 2.7–28.4°
c = 7.4709 (2) Å	µ = 2.53 mm^−1
β = 94.645 (1)°	T = 233 K
V = 1742.05 (9) Å^3	Slab, colourless
Z = 4	0.36 × 0.28 × 0.16 mm
F(000) = 816

Data collection

Siemens SMART CCD area-detector diffractometer	4173 independent reflections
Radiation source: fine-focus sealed tube	2016 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.080
Detector resolution: 8.33 pixels mm^-1	θmax = 28.3°, θmin = 2.7°
ω scans	h = −23→24
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996)	k = −16→13
Tmin = 0.463, Tmax = 0.688	l = −9→9
10113 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.050	H-atom parameters constrained
wR(F^2) = 0.120	w = 1/[σ^2(Fo^2) + (0.0153P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.81	(Δ/σ)max < 0.001
4173 reflections	Δρmax = 0.45 e Å^−3
219 parameters	Δρmin = −0.76 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0091 (10)

Special details

Experimental. The data collection covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle (0, 88 and 180°) for the crystal and each exposure of 30 s covered 0.3° in ω. The crystal-to-detector distance was 5 cm and the detector swing angle was -35°. Crystal decay was monitored by repeating 50 initial frames at the end of data collection and analysing the intensity of duplicate reflections, and was found to be negligible.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.01467 (2)	0.17658 (4)	0.02239 (7)	0.0871 (2)
Cl1	0.38225 (4)	0.06873 (6)	0.14071 (12)	0.0535 (3)
N1	0.25402 (12)	−0.13389 (18)	0.5294 (3)	0.0341 (6)
O1	0.24139 (12)	0.03406 (17)	0.6532 (3)	0.0555 (6)
O2	0.38958 (11)	0.06516 (17)	0.5772 (3)	0.0501 (6)
O3	0.18197 (14)	−0.2778 (2)	0.5427 (4)	0.0783 (8)
C1	0.27250 (16)	−0.0274 (2)	0.5641 (4)	0.0353 (7)
C2	0.31508 (15)	−0.1864 (2)	0.4589 (4)	0.0335 (7)
C3	0.32712 (18)	−0.2932 (2)	0.4324 (4)	0.0431 (8)
H3	0.2920	−0.3436	0.4517	0.052*
C4	0.3933 (2)	−0.3223 (3)	0.3762 (4)	0.0489 (9)
H4	0.4025	−0.3938	0.3572	0.059*
C5	0.44571 (19)	−0.2491 (3)	0.3476 (4)	0.0508 (9)
H5	0.4897	−0.2716	0.3099	0.061*
C6	0.43368 (16)	−0.1421 (3)	0.3744 (4)	0.0436 (8)
H6	0.4692	−0.0921	0.3559	0.052*
C7	0.36768 (14)	−0.1113 (2)	0.4291 (4)	0.0338 (7)
C8	0.34101 (15)	−0.0042 (2)	0.4713 (4)	0.0355 (7)
C9	0.32712 (15)	0.0872 (2)	0.3264 (4)	0.0354 (7)
C10	0.36599 (17)	0.1576 (2)	0.4714 (5)	0.0516 (9)
H10A	0.4055	0.1981	0.4286	0.062*
H10B	0.3336	0.2036	0.5314	0.062*
C11	0.25103 (15)	0.1110 (2)	0.2527 (4)	0.0354 (7)
C12	0.22197 (17)	0.2117 (2)	0.2610 (4)	0.0425 (8)
H12	0.2497	0.2664	0.3142	0.051*
C13	0.15194 (18)	0.2320 (3)	0.1910 (5)	0.0534 (9)
H13	0.1329	0.3002	0.1950	0.064*
C14	0.11113 (17)	0.1500 (3)	0.1158 (5)	0.0504 (9)
C15	0.13853 (18)	0.0483 (3)	0.1064 (5)	0.0537 (9)
H15	0.1102	−0.0065	0.0557	0.064*
C16	0.20849 (17)	0.0300 (3)	0.1736 (5)	0.0471 (8)
H16	0.2278	−0.0378	0.1662	0.057*
C17	0.18800 (18)	−0.1837 (3)	0.5626 (5)	0.0516 (9)
C18	0.12870 (19)	−0.1140 (3)	0.6140 (7)	0.0818 (13)
H18A	0.1190	−0.0606	0.5235	0.123*
H18B	0.1427	−0.0805	0.7269	0.123*
H18C	0.0860	−0.1557	0.6249	0.123*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0510 (3)	0.1050 (4)	0.1027 (4)	0.0141 (2)	−0.0112 (2)	0.0170 (3)
Cl1	0.0560 (5)	0.0370 (5)	0.0711 (6)	−0.0002 (4)	0.0275 (4)	0.0051 (4)
N1	0.0326 (13)	0.0255 (14)	0.0441 (15)	−0.0047 (10)	0.0028 (11)	0.0020 (11)
O1	0.0603 (15)	0.0355 (13)	0.0737 (17)	0.0005 (11)	0.0230 (13)	−0.0104 (12)
O2	0.0469 (13)	0.0430 (14)	0.0586 (14)	−0.0111 (10)	−0.0074 (10)	−0.0124 (12)
O3	0.0686 (18)	0.0375 (16)	0.131 (2)	−0.0204 (13)	0.0196 (16)	0.0006 (16)
C1	0.0385 (16)	0.0250 (16)	0.0415 (18)	0.0022 (13)	−0.0012 (13)	0.0002 (14)
C2	0.0369 (16)	0.0275 (16)	0.0347 (16)	0.0036 (12)	−0.0050 (13)	0.0016 (13)
C3	0.060 (2)	0.0280 (18)	0.0402 (18)	0.0028 (15)	−0.0041 (15)	0.0004 (14)
C4	0.073 (3)	0.0323 (19)	0.0401 (19)	0.0185 (17)	−0.0041 (17)	−0.0001 (15)
C5	0.051 (2)	0.057 (2)	0.0434 (19)	0.0285 (18)	−0.0014 (15)	−0.0016 (17)
C6	0.0347 (17)	0.053 (2)	0.0417 (18)	0.0040 (15)	−0.0035 (14)	0.0020 (16)
C7	0.0321 (15)	0.0313 (17)	0.0367 (16)	0.0029 (12)	−0.0055 (12)	0.0007 (13)
C8	0.0313 (16)	0.0287 (17)	0.0457 (18)	−0.0060 (12)	−0.0011 (13)	−0.0068 (14)
C9	0.0345 (16)	0.0215 (16)	0.0512 (19)	−0.0033 (12)	0.0103 (13)	−0.0054 (13)
C10	0.0425 (19)	0.0313 (19)	0.081 (3)	−0.0118 (14)	0.0027 (17)	−0.0172 (18)
C11	0.0402 (16)	0.0214 (15)	0.0454 (18)	0.0001 (13)	0.0082 (13)	0.0028 (13)
C12	0.0495 (19)	0.0242 (17)	0.054 (2)	−0.0021 (14)	0.0073 (15)	0.0013 (15)
C13	0.056 (2)	0.0331 (19)	0.072 (2)	0.0101 (16)	0.0122 (18)	0.0103 (18)
C14	0.0401 (18)	0.057 (2)	0.054 (2)	0.0056 (16)	−0.0005 (15)	0.0129 (18)
C15	0.051 (2)	0.046 (2)	0.062 (2)	−0.0065 (17)	−0.0089 (17)	−0.0049 (18)
C16	0.0490 (19)	0.0289 (18)	0.062 (2)	0.0031 (15)	−0.0023 (16)	−0.0029 (16)
C17	0.046 (2)	0.044 (2)	0.066 (2)	−0.0104 (16)	0.0084 (17)	0.0072 (18)
C18	0.042 (2)	0.066 (3)	0.140 (4)	−0.0086 (19)	0.025 (2)	−0.006 (3)

Geometric parameters (Å, º)

Br1—C14	1.900 (3)	C7—C8	1.479 (4)
Cl1—C9	1.805 (3)	C8—C9	1.587 (4)
N1—C1	1.403 (4)	C9—C11	1.505 (4)
N1—C17	1.418 (4)	C9—C10	1.535 (4)
N1—C2	1.448 (4)	C10—H10A	0.9700
O1—C1	1.200 (3)	C10—H10B	0.9700
O2—C8	1.445 (3)	C11—C12	1.380 (4)
O2—C10	1.455 (4)	C11—C16	1.392 (4)
O3—C17	1.198 (4)	C12—C13	1.386 (4)
C1—C8	1.526 (4)	C12—H12	0.9300
C2—C3	1.380 (4)	C13—C14	1.374 (5)
C2—C7	1.390 (4)	C13—H13	0.9300
C3—C4	1.380 (4)	C14—C15	1.382 (5)
C3—H3	0.9300	C15—C16	1.375 (4)
C4—C5	1.370 (5)	C15—H15	0.9300
C4—H4	0.9300	C16—H16	0.9300
C5—C6	1.383 (4)	C17—C18	1.484 (5)
C5—H5	0.9300	C18—H18A	0.9600
C6—C7	1.379 (4)	C18—H18B	0.9600
C6—H6	0.9300	C18—H18C	0.9600
C1—N1—C17	126.4 (3)	C10—C9—Cl1	110.7 (2)
C1—N1—C2	108.4 (2)	C8—C9—Cl1	111.10 (18)
C17—N1—C2	125.2 (2)	O2—C10—C9	91.4 (2)
C8—O2—C10	92.2 (2)	O2—C10—H10A	113.4
O1—C1—N1	126.7 (3)	C9—C10—H10A	113.4
O1—C1—C8	125.9 (3)	O2—C10—H10B	113.4
N1—C1—C8	107.4 (2)	C9—C10—H10B	113.4
C3—C2—C7	121.0 (3)	H10A—C10—H10B	110.7
C3—C2—N1	129.6 (3)	C12—C11—C16	118.7 (3)
C7—C2—N1	109.2 (2)	C12—C11—C9	121.7 (3)
C4—C3—C2	117.5 (3)	C16—C11—C9	119.5 (2)
C4—C3—H3	121.3	C11—C12—C13	120.7 (3)
C2—C3—H3	121.3	C11—C12—H12	119.6
C5—C4—C3	122.1 (3)	C13—C12—H12	119.6
C5—C4—H4	119.0	C14—C13—C12	119.1 (3)
C3—C4—H4	119.0	C14—C13—H13	120.5
C4—C5—C6	120.5 (3)	C12—C13—H13	120.5
C4—C5—H5	119.8	C13—C14—C15	121.6 (3)
C6—C5—H5	119.8	C13—C14—Br1	119.4 (3)
C7—C6—C5	118.3 (3)	C15—C14—Br1	119.0 (3)
C7—C6—H6	120.8	C16—C15—C14	118.6 (3)
C5—C6—H6	120.8	C16—C15—H15	120.7
C6—C7—C2	120.7 (3)	C14—C15—H15	120.7
C6—C7—C8	129.8 (3)	C15—C16—C11	121.3 (3)
C2—C7—C8	109.5 (2)	C15—C16—H16	119.3
O2—C8—C7	117.6 (2)	C11—C16—H16	119.3
O2—C8—C1	111.9 (2)	O3—C17—N1	119.3 (3)
C7—C8—C1	103.2 (2)	O3—C17—C18	123.6 (3)
O2—C8—C9	89.71 (19)	N1—C17—C18	117.0 (3)
C7—C8—C9	123.7 (3)	C17—C18—H18A	109.5
C1—C8—C9	110.7 (2)	C17—C18—H18B	109.5
C11—C9—C10	121.1 (2)	H18A—C18—H18B	109.5
C11—C9—C8	119.4 (2)	C17—C18—H18C	109.5
C10—C9—C8	84.1 (2)	H18A—C18—H18C	109.5
C11—C9—Cl1	108.6 (2)	H18B—C18—H18C	109.5
C17—N1—C1—O1	13.2 (5)	O2—C8—C9—C11	−134.3 (2)
C2—N1—C1—O1	−164.8 (3)	C7—C8—C9—C11	102.2 (3)
C17—N1—C1—C8	−168.2 (3)	C1—C8—C9—C11	−20.8 (3)
C2—N1—C1—C8	13.8 (3)	O2—C8—C9—C10	−11.7 (2)
C1—N1—C2—C3	168.4 (3)	C7—C8—C9—C10	−135.3 (3)
C17—N1—C2—C3	−9.6 (5)	C1—C8—C9—C10	101.7 (3)
C1—N1—C2—C7	−7.1 (3)	O2—C8—C9—Cl1	98.2 (2)
C17—N1—C2—C7	174.8 (3)	C7—C8—C9—Cl1	−25.4 (3)
C7—C2—C3—C4	0.3 (4)	C1—C8—C9—Cl1	−148.4 (2)
N1—C2—C3—C4	−174.8 (3)	C8—O2—C10—C9	−12.7 (2)
C2—C3—C4—C5	0.2 (5)	C11—C9—C10—O2	132.5 (3)
C3—C4—C5—C6	−0.1 (5)	C8—C9—C10—O2	11.6 (2)
C4—C5—C6—C7	−0.4 (5)	Cl1—C9—C10—O2	−98.7 (2)
C5—C6—C7—C2	0.9 (4)	C10—C9—C11—C12	22.9 (4)
C5—C6—C7—C8	178.5 (3)	C8—C9—C11—C12	124.5 (3)
C3—C2—C7—C6	−0.8 (4)	Cl1—C9—C11—C12	−106.8 (3)
N1—C2—C7—C6	175.2 (2)	C10—C9—C11—C16	−157.2 (3)
C3—C2—C7—C8	−178.8 (3)	C8—C9—C11—C16	−55.6 (4)
N1—C2—C7—C8	−2.8 (3)	Cl1—C9—C11—C16	73.1 (3)
C10—O2—C8—C7	140.8 (3)	C16—C11—C12—C13	−0.4 (4)
C10—O2—C8—C1	−99.9 (3)	C9—C11—C12—C13	179.5 (3)
C10—O2—C8—C9	12.3 (2)	C11—C12—C13—C14	1.2 (5)
C6—C7—C8—O2	−43.4 (4)	C12—C13—C14—C15	−0.8 (5)
C2—C7—C8—O2	134.4 (3)	C12—C13—C14—Br1	179.2 (2)
C6—C7—C8—C1	−167.1 (3)	C13—C14—C15—C16	−0.3 (5)
C2—C7—C8—C1	10.7 (3)	Br1—C14—C15—C16	179.7 (3)
C6—C7—C8—C9	66.6 (4)	C14—C15—C16—C11	1.1 (5)
C2—C7—C8—C9	−115.6 (3)	C12—C11—C16—C15	−0.8 (5)
O1—C1—C8—O2	36.3 (4)	C9—C11—C16—C15	179.3 (3)
N1—C1—C8—O2	−142.3 (2)	C1—N1—C17—O3	−172.8 (3)
O1—C1—C8—C7	163.7 (3)	C2—N1—C17—O3	4.9 (5)
N1—C1—C8—C7	−14.9 (3)	C1—N1—C17—C18	9.5 (5)
O1—C1—C8—C9	−62.1 (4)	C2—N1—C17—C18	−172.8 (3)
N1—C1—C8—C9	119.3 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···O3	0.93	2.36	2.890 (4)	116